On stability in linear feedback circuits

In this paper, the precise relations defining system transfer and stability functions and system phase margin are developed. These functions account for loading at input and output ports of the amplifying block due to the feedback element. They are derived using the analysis methodology of Driving Point Impedance/Signal Flow Graphs (DPI/SFG) recently introduced. With this process, stability relations are obtained from closed loop SPICE simulations removing all questions about opening loops. A summary of the DPI/SFG method is given.